A LARGE SCALE ELECTRICAL SURVEY TO MAP CONCEALED ANTIQUITIES IN MARATHON

• G. N. Tsokas, P. I. Tsourlos, A. Stampolidis, G. Vargemezis (Geophysical Laboratory, Dept. of Geology, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece)
• G. Steinhauer (B' Ephorate of Prehistoric and Classic Antiquities, Polygnotou 13, 105 55 Athens, Greece)

A large-scale geophysical survey was carried out at the foothills of a topographic table hosting the ruins of the ancient city "Trikorinthos", in the area of Marathon north of Athens. The explored site assumed to host remnants of ancient constructions belonging to the ancient city. Although the explored site is associated with the final phase of the famous Marathon battle, it did not expected to bear any signs of that event.

A total area of about 10000 m² was covered by resistivity tomographies and about 5500 m² were explored by resistivity mapping. The distance between the measured electrical sections was 0.6 to 2.4 m, resulting into a large number of tomographic data. Such an extensive application of electrical tomographic imaging in archaeological site investigation renders the present survey as one of the largest worldwide. The Schlumberger and pole -dipole arrays were used, having the electrodes spaced at 0.6 m. The instrumentation allowed to use 42 channels in each spread and resulted to 144 measurements for each tomography. Resistivity mapping was conducted along profiles spaced 1 m apart, stepwise at 1 m intervals.

The interpretation of the tomographic data was conducted using the inversion scheme of Tsoulros (1995). This is based on a fully non-linear smoothness constrained inversion scheme, which uses a finite element forward problem solver (Tsourlos et al. 1995).

The inverted data was combined to produce depth slices and 3-D images. An example is given in Figure 1. The whole operation resulted in detecting and mapping various concealed structures, some of which were verified by the subsequent excavation. Therefore, the ancient use of the area is revealed by the combined result of the geophysical investigation and digging.

Tsourlos P., 1995. Modelling interpretation and inversion of multielectrode resistivity survey data. Ph.D. Thesis, University of York.

Tsourlos P., Dittmer J. and Szymanski J. (1995). A study of non-linear techniques for the 2-D inversion of earth resistivity data. Expanded abstracts of the 57th meeting of the EAEG: Glasgow, Scotland, 29 May-2 June, 1995.